Know what you mean about them catching you despite consistent foalwatching - they wait til I've just walked away and the tail goes up, feet come out and all systems go! I've got a bit sneaky over the years, foalcam watching or other tactics to sneak back unexpectedly and it is something of a game with one or two of them now, I'm sure
Still worth it all when you get a healthy foal up and running tho, whatever names you grumble at the time